U.S. patent number 4,785,689 [Application Number 06/945,483] was granted by the patent office on 1988-11-22 for failsafe system in automatic transmission.
This patent grant is currently assigned to Toyota Jidosha Kabushiki Kaisha. Invention is credited to Kunihiro Iwatsuki, Yoshio Shindo.
United States Patent |
4,785,689 |
Iwatsuki , et al. |
November 22, 1988 |
Failsafe system in automatic transmission
Abstract
A failsafe system in an automatic transmission includes: a
device for detecting rotary speed of an output shaft of the
automatic transmission; a device for detecting either rotary speed
of a rotary member other than the output shaft of the automatic
transmission or engine rotary speed. When a correlation between the
output shaft rotary speed and either the rotary speed of the rotary
member or the engine rotary speed is abnormal, control oil pressure
in a hydraulic control device of the automatic transmission is
increased, whereby slippage in frictionally engaging devices in the
hydraulic control device of the automatic transmission during
non-shift are effectively eliminated.
Inventors: |
Iwatsuki; Kunihiro (Toyota,
JP), Shindo; Yoshio (Toyota, JP) |
Assignee: |
Toyota Jidosha Kabushiki Kaisha
(Aichi, JP)
|
Family
ID: |
17769144 |
Appl.
No.: |
06/945,483 |
Filed: |
December 23, 1986 |
Foreign Application Priority Data
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|
|
|
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Dec 24, 1985 [JP] |
|
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60-291459 |
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Current U.S.
Class: |
477/161; 192/30W;
477/62; 477/906 |
Current CPC
Class: |
F16H
61/0021 (20130101); F16H 61/12 (20130101); F16H
59/46 (20130101); F16H 61/686 (20130101); F16H
2059/465 (20130101); F16H 2061/0462 (20130101); F16H
59/38 (20130101); F16H 59/40 (20130101); Y10S
477/906 (20130101); Y10T 477/635 (20150115); Y10T
477/693964 (20150115) |
Current International
Class: |
F16H
61/12 (20060101); F16H 61/00 (20060101); F16H
59/38 (20060101); F16H 59/46 (20060101); F16H
59/40 (20060101); B60K 041/06 () |
Field of
Search: |
;74/866,867,862,865,856
;192/3W |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2125178 |
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Nov 1972 |
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DE |
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136415 |
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Jul 1979 |
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DE |
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36611 |
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Mar 1980 |
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JP |
|
49450 |
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May 1981 |
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JP |
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49447 |
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May 1981 |
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JP |
|
173647 |
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Oct 1982 |
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JP |
|
9356 |
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Jan 1984 |
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JP |
|
11753 |
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Jan 1985 |
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JP |
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92931 |
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May 1985 |
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JP |
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2084673 |
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Apr 1982 |
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GB |
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Primary Examiner: Braun; Leslie A.
Assistant Examiner: Diehl; Dwight G.
Attorney, Agent or Firm: Parkhurst, Oliff & Berridge
Claims
What is claimed is:
1. A failsafe system in an automatic transmission for a vehicle,
comprising:
means for detecting an output shaft rotary speed of said automatic
transmission;
means for detecting engine rotary speed;
means for detecting engine load;
means for detecting whether a lockup clutch of said automatic
transmission is engaged;
means for detecting whether a prescribed period of time has elapsed
from either a shift judgment or a shift command of said automatic
transmission;
means for determining a correlation between said output shaft
rotary speed and said engine rotary speed when said engine load is
higher than a predetermined value, said lockup clutch is engaged,
and said prescribed period of time has elapsed from either of said
shift judgment or shift command of said automatic transmission;
means for judging whether said correlation is abnormal; and
means for increasing oil pressure in a hydraulic control device of
said automatic transmission when said correlation is judged to be
abnormal.
2. The failsafe system as set forth in claim 1, wherein said oil
pressure in the hydraulic control device is line pressure.
3. The failsafe system as set forth in claim 1, further
comprising:
an electromagnetic proportion valve; wherein said oil pressure in
the hydraulic control device is increased by the control of said
electromagnetic proportion valve.
4. The failsafe system as set forth in claim 1, further
comprising:
a duty valve; wherein said oil pressure in the hydraulic control
device is increased by the duty control of said duty valve.
5. The failsafe system as set forth in claim 1, further
comprising:
means for judging whether said correlation is shifted more than a
predetermined value; wherein said judging means judges said
correlation is abnormal when said correlation is shifted more than
said predetermined value.
6. The failsafe system as set forth in claim 1, further
comprising:
means for judging whether said correlation is shifted more than a
predetermined value for a predetermined period of time; wherein
said judging means judges said correlation is abnormal when said
correlation is shifted more than said predetermined value for a
predetermined period of time.
7. The failsafe system as set forth in claim 1, further
comprising:
a warning device; wherein, when said correlation is judged to be
abnormal, a warning is issued from said warning device.
8. A failsafe system in an automatic transmission for a vehicle,
comprising:
means for detecting rotary speed of an output shaft of said
automatic transmission;
means for detecting rotary speed of a turbine shaft of said
automatic transmission;
means for detecting engine load;
means for detecting whether a prescribed period of time has elapsed
from either a shift judgment or a shift command of said automatic
transmission;
means for determining a correlation between the rotary speed of the
output shaft and the rotary speed of the turbine shaft when said
engine load is higher than a predetermined value, and said
prescribed period of time has elapsed from either of said shift
judgment or shift command of said automatic transmission;
means for judging whether said correlation is abnormal; and
means for increasing oil pressure in a hydraulic control device of
said automatic transmission when said correlation is judged to be
abnormal.
Description
BACKGROUND OF THE INVENTION
This invention relates to a failsafe system in an automatic
transmission.
Vehicle automatic transmissions having a gear shift mechanism, a
plurality of frictionally engaging devices and a hydraulic control
device to selectively engage the frictionally engaging devices to
set various gear stages are well known in the art.
The conventional frictionally engaging device is comprised of two
sets of relatively rotatably friction plate elements and a
hydraulic servo device for driving the friction plate elements.
When oil pressure is fed to the hydraulic servo device, the two
sets of the friction plate elements are strongly urged together, so
that the friction plate elements frictionally engage with
sufficient force to transmit torque therebetween.
The lower limit for the control oil pressure to the frictionally
engaging device of the type described is the pressure wherein:
(1) all of the gear stages in all of the shift positions can be
achieved irrespective of engine load (an engine output), vehicle
speed or the like, i.e. the pressure giving rise to a torque
capacity which precludes slippage of the frictionally engaging
devices during non-shift running: (2) the pressure giving rise to a
torque capacity resulting in completion of shifting within a
predetermined period of time so as not to damage the frictionally
engaging devices during shifting from excess slippage.
In general, the working oil pressure to the frictionally engaging
devices is a line pressure. In view of the above-described lower
oil pressure limits, line pressure has heretofore been controlled
in accordance with a value normally regarded as typifying an engine
load, such as, for example, engine throttle opening. More
specifically, the control is carried out such that line pressure
increases with increasing engine loads.
In prior art devices, a throttle pressure related to the throttle
opening is introduced into a control port of a primary regulator
valve to control the line pressure. This throttle pressure has been
generated by a throttle valve, to which a resilient force
increasing with accelerator pedal depression is applied. In recent
years, electronically-driven automatic transmission have been
developed, whereby essential portions of the control circuit
implement electronic circuitry. In the electronically-driven
automatic transmissions of this type, information on the throttle
opening is processed in the form of an electric signal, whereby the
line pressure is controlled in response to an electric signal
relating to the throttle opening (For example, in Japanese Utility
Model Kokai (Laid-Open) No. 125555/1981).
When it becomes possible to control the line pressure or the
throttle pressure by a command from a computer as described above,
highly detailed control can be carried out as suggested in a
related Japanese Patent Application No. 263131/1985 (filing date:
Nov. 22, 1985) for example. More specifically, during non-shift
running, the line pressure can be lowered as much as possible in
accordance with engine load, vehicle speed and the like, with an
appropriate extra margin of safety being kept, to thereby avoid
wasteful powerloss suffered by a pump (precise control of a
condition 1) for determining the lower limit of the aforesaid
control oil pressure.
However, when control oil pressure given to the frictionally
engaging devices is controlled by a command from a computer in
response to input signals from the various sensors as described
above, if there occur malfunctions in a sensor system,
short-circuits in the sensor system and a computer input system,
unexpected leakage of oil pressure in a hydraulic control device of
the automatic transmission, unexpected rise in engine output, and
the like, then slips occur in the frictinally engaging devices,
whereby the gear stage cannot be suitably maintained, thus possibly
deteriorating durability of the frictionally engaging devices.
SUMMARY OF THE INVENTION
The present invention has been developed to obviate the
above-described disadvantages of the prior art and has its object
the provision of a failsafe system in an automatic transmission,
wherein, even if such unexpected situations as described above
occur, control oil pressure in the hydraulic control device can be
raised rapidly to a suitable value and durability of frictionally
engaging devices can be secured and improved.
To achieve the above-described object, as the technical
illustration thereof is shown in FIG. 1, the present invention
detects rotary speed of an output shaft of the automatic
transmission and detects either rotary speed of a rotary member
other than the output shaft of the automatic transmission or engine
rotary speed. Further, the present invention judges normality or
abnormality of a correlation between the rotary speed of the output
shaft and the rotary speed of above rotary member, or between the
rotary speed of the output shaft and the engine rotary speed. The
correlation is defined in association with a gear ratio of a gear
stage of the automatic transmission. When the correlation is judged
to be abnormal, oil pressure in the hydraulic control device of the
automatic transmission is increased.
According to the present invention, when the correlation is
abnormal, i.e. the frictionally engaging devices are slipping,
whereby the correlation therebetween is shifted from the
relationship which should properly be, the oil pressure in the
hydraulic control device of the automatic transmission is
increased. As a result, even when the control oil pressure is
lowered due to a trouble in the sensor system or the like, whereby
slips occur in the frictionally engaging devices, this situation is
rapidly detected, so that the proper state can be rapidly restored.
Consequently, deteriorated durability of the frictionally engaging
devices can be avoided and more stabilized running can be
performed.
The preferred embodiment is of such an arrangement that the oil
pressure in the hydraulic control device is the line pressure. This
is because the oil pressure acting on the frictionally engaging
devices during non-shift running is basically dependent upon the
line pressure.
Furthermore, it is preferable that the oil pressure in the
hydraulic control device is increased by the control of an
electromagnetic proportion valve. Or, the oil pressure in the
hydraulic control device is increased by the duty control. For the
control of the electromagnetic proportion valve or the duty control
itself, well known means is adoptable.
Furthermore, it is preferable that, when the correlation is shifted
by a predetermined value or more, the correlation should be judged
to be abnormal. With this arrangement, errors in a detecting system
can be absorbed.
Furthermore, it is preferable that, when the correlation is shifted
larger than the predetermined value for a predetermined period of
time, the correlation should be judged to be abnormal. With this
arrangement, such a misjudgment that an instantaneous shift in the
correlation is erroneously attributed to the slips of the
frictionally engaging devices can be avoided.
Furthermore, it is preferable that, when the correlation is judged
to be abnormal, a warning is issued. With this arrangement, a
driver is informed that the failsafe function according to the
present invention is performing, and rapid inspection and the like
can be urged.
Furthermore, it is preferable that the correlation is judged when
the engine load is higher than a predetermined value.
Furthermore, it is preferable that the correlation is judged when a
lockup clutch is engaged.
Furthermore, it is preferable that the correlation is judged after
a lapse of a prescribed period of time from either a shift judgment
or a shift command.
Judgment of failsafe need not necessarily be made for the entire
period of time, and, malfunction of the failsafe function is
avoided more often when the correlation can be more steadily
grasped. As a consequence, from this point of view, for example,
judgment of the correlation may preferably be made when the engine
load is higher than a predetermined value (when no engine brake is
operating), the lockup clutch is engaged, and after a lapse of a
prescribed period of time from either a shift judgment or a shift
command.
BRIEF DESCRIPTION OF THE DRAWINGS
The above object, features and advantages of the present invention,
as well as other objects and advantages thereof, will become more
apparent from the description of the invention which follows, taken
in conjunction with the accompanying drawings, wherein like
reference characters designate the same or similar parts and
wherein:
FIG. 1 is a block diagram showing the technical illustration of the
present invention;
FIG. 2 is a skeleton diagram showing the general arrangement of the
automatic transmission, to which one embodiment of the failsafe
system of the automatic transmission for a vehicle according to the
present invention is applied;
FIG. 3 is a chart showing the operating conditions of the
frictinally engaging devices in the above automatic
transmission;
FIG. 4 is a chart showing the input and output relationship of the
control system;
FIG. 5 is a hydraulic circuit diagram showing the essential
portions of the hydraulic control device;
FIG. 6 is a flow chart showing a control routine;
FIG. 7 is a chart showing the relationship between a correlation
difference .DELTA.Nt and a corrected current value .DELTA.Ip of the
electromagnetic proportion valve;
FIG. 8 is a flow chart showing an example of another control
routine; and
FIG. 9 is a hydraulic circuit diagram showing the essential
portions of a hydraulic control device to explain another means for
changing the line pressure.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention, which can be illustrated by FIG. 1, will be
described in detail with reference to other accompanying drawings
which illustrate preferred embodiments of the present
invention.
FIG. 2 shows the outline of the general arrangement of the
automatic transmission for a vehicle to which this embodiment is
applied.
The automatic transmission includes a torque converter 20, an
overdrive mechanism 40 and an underdrive mechanism 60 including
three forward gear stages and one reverse gear stage.
The torque converter 20 is of a type well known in the art, and
includes a pump 21, a turbine 22, a stator 23 and a lockup clutch
24. The pump 21 is connected to a crankshaft 10 of an engine 1. The
turbine 22 is connected to a carrier 41 of planetary gear trains in
the overdrive mechanism 40 through a turbine shaft 22A.
In the overdrive mechanism 40, a planetary pinion 42 rotatably
supported by carrier 41 is in meshing engagement with a sun gear 43
and a ring gear 44. A clutch C0 and a one-way clutch F0 are
provided between the sun gear 43 and the carrier 41. A brake B0 is
interposed between the sun gear 43 and a housing Hu.
The underdrive mechanism 60 is provided with front and rear
planetary gear trains. The two planetary gear trains include a
common sun gear 61, ring gears 62 and 63, planetary pinions 64 and
65, and carriers 66 and 67.
The ring gear 44 in the overdrive mechanism 40 is connected to the
ring gear 62 through a clutch C1. A clutch C2 is interposed between
the ring gear 44 and the sun gear 61. The carrier 66 is connected
to the ring gear 63. The carrier 66 and the ring gear 63 are
connected to an output shaft 70.
A brake B3 and a one-way clutch F2 are interposed between the
carrier 67 and the housing Hu. A brake B2 and a one-way clutch F1
are provided between the sun gear 61 the housing Hu. A brake B1 is
interposed between the sun gear 61 and the housing Hu.
The automatic transmission of this embodiment is provided with a
computer (ECU) 84 receiving input signals from a throttle sensor 80
for detecting a throttle opening reflecting a load of the engine 1,
from a vehicle speed sensor 82 for detecting a vehicle speed, and a
from a turbine sensor 83 for detecting rotary speed of turbine
shaft 22A, and the like. Computer 84 controls solenoid valves S1
and S2 (for controlling shift valves), solenoid valve SL (for
controlling the lockup clutch) and an electromagnetic proportion
valve SD (for controlling the line pressure) in a hydraulic control
device 86 in accordance with a preset shift map. As a result,
combinations of engagements between the clutches, the brakes and
the like as shown in FIG. 3 are performed to thereby carry out
shift controls. In FIG. 3 marks .circle. indicate engaged
conditions and marks .circleincircle. indicate engaged conditions
only when no engine brake is operating.
As shown in FIG. 4, the solenoid valve S1 controls a 2-3 shift
valve. The solenoid valve S2 controls a 1-2 shift valve and a 3-4
shift valve. The 1-2 and the 2-3 shift valves perform the
shift-control from 1st gear stage to 3rd gear stage in the
underdrive mechanism 60. The 3-4 shift valve performs the
shift-control in the overdrive mechanism 40 (shifts between 3rd
gear stage and 4th gear stage). The solenoid valve SL performs the
control of a lockup clutch 24 in the torque converter 20 through a
lockup relay valve. The electromagnetic proportion valve SD
performs the control of the line pressure in the hydraulic control
device 86 through a primary regulator valve (described below).
Additionally, in FIG. 2, designated at 90 is a shift position
sensor to detect the selected shift position (e.g., N, D, R and the
like), 92 is a pattern select switch to select E (economical
running), P (power running) or the like, 94 is an engine water
temperature sensor to detect the water temperature of the engine,
96 is a foot brake switch to detect foot brake actuation, and 98 is
a brake switch to detect side brake actuation, respectively.
FIG. 5 shows the essential portions of the hydraulic control device
86.
In the drawing, denoted at SD is the electromagnetic proportion
valve, at 102 is a pump directly connected to the engine, at 103 is
the primary regulator valve for regulating the line pressure, at
104 a 1-2 shift valve for changing over between a first gear stage
and second gear stage, at S2 is the solenoid valve for controlling
the 1-2 shift valve, at 105 is a secondary regulator valve for
supplying the lubricating oil, at 106 is a manual valve operated by
the driver and at 107 is an accumulator for controlling the
transition characteristics when the oil pressure is supplied to or
removed from the brake B2, respectively.
The electromagnetic proportion valve SD is well known by itself and
includes spools 109 and 110, coil 108, spring 113, plunger 111 and
the like. The spool 110 and the plunger 111 are interconnected in
the axial direction. The coil 108 applies a force Fc directed
downwardly in the drawing to the plunger 111 (and the spool 110) in
accordance with load current Ip from the ECU 84. On opposition to
the force Fc, the spring 113 renders a force Fs to the spool 110. A
discharge pressure from the pump 102 acts on a port 109A. The oil
pressure at ports 115 and 116 is designated PQ. PQ is derived
through the following equation (1), wherein A1 is the surface area
of land 109A of spool 109.
As a consequence, the force Fc directed downwardly in the drawing,
which is generated by the coil 108, is controlled, so that the oil
pressure PQ generated at the port 115 in accordance with equation
(1) can be controlled to a desirable value ranging from zero to
Fs/A1. Oil pressure PQ corresponds to a so-called throttle pressure
which has heretofore been normally generated by a throttle valve,
wherein a spool is mechanically drivable through a cam in
proportion to a throttle opening. Oil pressure PQ acts on a port
119 of a primary regulator valve 103 to control the line pressure.
Oil pressure PQ also acts on a port 153 of a secondary regulator
valve 105 to control the lubricating oil pressure.
In the primary regulator valve 103, the line pressure PL is
generated in relation to the value of the control pressure PQ, as
is conventional. Because the load current Ip to the coil 108 is
controlled in response to a command from the ECU 84, the line
pressure PL can be desirably controlled. The equation relating to
the pressure regulation in the primary regulator valve 103 is as
follows:
wherein Fs2 is the acting force of a spring 120, H1-H3 are face
areas of lands 121, 122 and 125 of spools 123 and 124, and PR is
the line pressure applied to the lands 122 and 125 when the manual
valve 106 is in the reverse range.
The frictionally engaging devices are described below. The brake B2
will be described as typifying the frictionally engaging
devices.
A signal pressure of the solenoid valve S2 acts on port 126 of the
1-2 shift valve 104. As a consequence, a spool 127 of the 1-2 shift
valve 104 slides to the right and left in the drawing in accordance
with the ON-OFF operation of the solenoid valve S2. Spool 127 is
biased to the right due to the force Fs3 from a spring 128. When
spool 121 is in its rightward position, ports 133 and 129 in the
1-2 shift valve 104 communicate with one another. The line pressure
PL from a port 130 of the manual valve 106 acts on the port 129 in
the D (drive) range. More specifically, the ports 130, 129 and 133
are adapted to be connected to one another in the D range selection
position of the spool 131 of the manual valve 106. The port 133 is
connected to the brake B2 through an oil line 135 and a check valve
134. As a consequence, in the D range, the line pressure PL is
supplied to or removed from the brake B2 in accordance with the
ON-OFF operation of the solenoid valve S2.
The oil line 135 is connected with accumulator 107, whereby the
transitional oil pressure level is controlled when the line
pressure PL is supplied to or removed from the brake B2. The
transitional oil pressure PB2, i.e., the oil pressure while the
accumulator 107 is working, is derivable as a function of the line
pressure PL applied as the back pressure as indicated by the
following equation.
wherein Fs4 is an acting force of a spring 135, and K1 and K2 are
face areas of two lands of an accumulator piston 137.
Because the control oil pressure PQ is controlled by the load
current control to the electromagnetic proportion valve SD through
the above-described equations (1)-(3), the oil pressure PB2 to the
brake B2 can be derivably controlled at transitional times, as well
as other times.
FIG. 6 shows the control flow chart for above embodiment.
In Steps 202-206, a throttle opening As, rotary speed No of the
output shaft 70 (corresponding to vehicle speed) and rotary speed
Nt of the turbine shaft 22A are read in, respectively. Denoted at F
in Step 208 is a flag for controlling the flow. Since the flag F is
set at zero initially, the routine proceeds to Step 210, where the
occurrence of shift judgment is discriminated. When a shift
judgment occurs, the routine proceeds to Step 212, where a shift
output is carried out, the flag F is set to 1 in Step 214, a timer
t is cleared (started) in Step 216, and thereafter, reset is
made.
Thereafter, the routine proceeds to Steps 202-208 again, and since
F=1, in Step 218, judgment is made as to whether a prescribed
period of time TO from the timer start in Step 216 has elasped or
not. TO is selected to represent the minimum amount of time which
must elapse between a shift judgment or a shift command and the
determination of a correlation between the output shaft rotary
speed No and the turbine shaft rotary speed Nt. Until a passage of
time t reaches the prescribed time TO, reset is maintained and
judgment for the failsafe is not performed. When it is judged that
the passage of time t has reached the prescribed time TO, the flag
F is set to zero again in Step 220, and thereafter, reset is made.
The reason why the prescribed period of time TO from the shift
command is excluded from the period of time of judgment for a
failsafe as described above resides in that the correlation (to be
described hereunder) need not necessarily be established.
On the other hand, when no shifting is judged in Step 210, it is
discriminated whether a throttle opening As is higher than a
predetermined value Aso or not in Step 222. This is intended for
discriminating whether the engine brake is operating or not, and,
when the engine brake is operating (so-called coasting conditions),
the correlation is not necessarily be established in a certain gear
stage because a one-way clutch becomes free. When the throttle
opening As is lower than the predetermined value Aso in Step 222,
reset is made. When the throttle opening As is higher than the
predetermined value Aso, the routine proceeds to Step 223, 224,
where a calculated turbine shaft rotary speed Nto is calculated by
multiplying the output shaft rotary speed No by the gear ratio Ib
of the present gear stage. Subsequently, in Step 226, a correlation
difference .DELTA.Nt is calculated by subtracting the calculated
turbine shaft rotary speed Nto from an actual turbine shaft rotary
speed Nt.
In Step 228, judgment is made as to whether this correlation
difference .DELTA.Nt is larger than the predetermined value
.DELTA.Nto or not. When the correlation difference .DELTA.Nt is
smaller than the predetermined value .DELTA.Nto, it is regarded
that the frictionally engaging devices are functioning normaly by
the sufficient oil pressure, whereby, in Step 220, the flag F is
set to zero, and thereafter, reset is made.
On the other hand, when it is judged that the correlation
difference .DELTA.t is larger than the predetermined value
.DELTA.Nto, it is regarded that slips are generated in the
frictionally engaging devices, whereby, in Step 230, a corrected
current value .DELTA.Ip is determined in accordance with the
correlation difference .DELTA.Nt, current correction is made in
Step 232, thereafter, in Step 234, the flag F is set to 2, and a
warning is issued in Step 236.
After the flag F is set to 2 in Step 234, the routine proceeds from
Step 202-208 to Step 222, and check is repeated again. As a result,
this failsafe function is performed, having priority to shift
output based on the shift judgment. Additionally, FIG. 7 shows the
relationship between the correlation difference .DELTA.Nt and the
correction current value .DELTA.Ip in Step 230.
Needless to say, it should be an effective means to apply this
correction current value .DELTA.Ip as an offset value even at the
time of shifting.
FIG. 8 shows and example of another control flow. This control flow
is different from the preceding control flow in that subjects to be
detected for determining the correlation include the output shaft
rotary speed No and the engine rotary speed Ne. Along with this, in
Step 302, in place of the turbine shaft rotary speed Nt, the engine
rotary speed Ne is monitored, Nto, Nt, .DELTA.Nt, .DELTA.Nto are
replaced by Neo, Ne, .DELTA.Ne and .DELTA.Neo, in Steps 304, 306,
308 and 310, respectively, and, Step 312 is added after Step 222,
so that ON or OFF of the lockup clutch 24 is judged. This is
because, when the engine rotary speed Ne is selected as the subject
for determining the correlation, if the lockup clutch 24 is OFF,
then it is difficult to determine the correlation.
The above embodiment controls the oil pressure by the combination
of an electromagnetic proportion valve with a primary regulator
valve. However, the present disclosed invention is not so limited,
and may encompass further control systems for controlling oil
pressure. For example, as shown in the further embodiment of FIG.
9, in place of the electromagnetic proportion valve, a relief valve
141, a duty control valve 140 and a high speed solenoid valve 142
are provided. The duty ratio of the high speed solenoid valve 142
may be controlled to desirably regulate the line pressure applied
to a port 147 of the duty control valve 140 with the control oil
pressure PQ at a port 144. In this embodiment, port 147 is
connected to oil line point 136 shown in FIG. 5, the port 144 is
connected to port 119 of the primary regulator valve 103, and
further, a port 145 of the relief valve 141 is connected to the oil
line point 136. The regulation of pressure by such duty ratio
controls are disclosed the disclosures of Japanese Utility Model
Application Publication No. 38186/1983, Patent Kokai (Laid-Open)
No. 24246/1981 and the like, which disclosures are well known, and
expressly incorporated herein by reference.
Furthermore, it is applicable embodiment that only when the
correlation is shifted larger than the predetermined value for a
predetermined period of time, the correlation should be judged to
be abnormal. With this arrangement, such a misjudgment that an
instantaneous shift in the correlation is erroneously attributed to
the slips of the frictionally engaging devices can be avoided.
* * * * *